1. Field of the Invention
The present invention relates to an electrophoretic display device (EPD), and more particularly, to an electrophoretic display device suitable for a color EPD and a method of fabricating the same.
2. Description of the Related Art
In general, an electrophoretic display device is an image display device using a phenomenon that colloidal particles move to either one of the polarities when one pair of electrodes to which a voltage is applied are immersed into a colloidal solution. The electrophoretic display device has the characteristics of wide viewing angle, high reflectivity, low power consumption, and the like, without using a backlight and thus it may be expected to be widely used as an electronic paper.
The electrophoretic display device has a structure in which an electrophoretic film is interposed between two substrates, and at least one of the two substrates should be transparent to display an image in a reflective mode.
When a pixel electrode is formed on a lower substrate of the two substrates and a voltage is applied to the pixel electrode, charged particles within the electrophoretic film are moved to the pixel electrode or an opposite electrode thereof, thereby allowing an image to be observed through a viewing sheet.
Though not shown in the drawing, a typical electrophoretic display device has a structure in which an upper substrate having common electrode (not shown) and a lower substrate formed with pixel electrodes are disposed by facing each other, and an electrophoretic film is interposed between the two substrates.
Here, the electrophoretic film is composed of a solvent containing charged pigment particles, wherein microcapsules are formed by a coacervation method, and the electrophoretic film is formed by mixing the microcapsules in a binder and coating or laminating a base film.
Here, the pigment particles may be colored with different colors, and an image is expressed by adding pigments of black (B) and white (W), and the solvent and binder are formed with a transparent material, allowing light to be passed through.
In the foregoing electrophoretic film, pigment particles are surrounded by a microcapsule film, and thus pigment particles being moved to an undesired direction by a field of the adjacent pixel can be suppressed, thereby achieving a better image quality. At this time, a partition wall may be further provided between adjacent pixels to completely isolate a parasitic field.
In such a typical electrophoretic display device, when a voltage is applied to the pixel electrode, charged pigment particles are moved to an electrode having an opposite polarity thereto, thereby displaying a predetermined image according to the reflection of light caused by the pigment particles.
On the other hand, when they are moved to an electrode having a polarity charged by the pigment particles, another image will be displayed.
From this point of view, an electrophoretic display device according to the related art will be described below with reference to FIG. 1.
FIG. 1 is a plan view schematically illustrating an electrophoretic display device according to the related art, wherein one pixel is composed of four sub-pixels such as red (R), green (G), blue (B), and white (W) dots.
An electrophoretic display device according to the related art, as illustrated in FIG. 1, one pixel is composed of four red (R), green (G), blue (B), and white (W) sub-pixels. Furthermore, the red (R), green (G), and blue (B) sub-pixels are provided with red (R), green (G), and blue (B) color filters 65a, 65b, 65c, respectively, and the white sub-pixel is not provided with a color filter but defined as a white sub-pixel region 65d. 
Here, each of the red (R), green (G), and blue (B) sub-pixels has a thin-film transistor (not shown), and this thin-film transistor (not shown) is connected to a pixel electrode (not shown) in a matrix form.
Furthermore, the pixel electrodes formed on the red (R), green (G), and blue (B) sub-pixels, respectively, are formed with the same area as the area of the red (R), green (G), and blue (B) sub-pixels.
In the EPD having the foregoing construction, a panel having a quad-type color filter structure to which a white sub-pixel is added has been applied thereto in order to improve the problem of reduced white reflection rate in case of a color EPD that uses color filters.
A method of fabricating an EPD according to the related art in which a panel having a quad-type color filter structure to which a white sub-pixel is added is applied thereto will be described below with reference to FIG. 2.
FIG. 2 is a cross-sectional view schematically illustrating an electrophoretic display device according to the related art, wherein one pixel is composed of four sub-pixels such as red (R), green (G), blue (B), and white (W) dots.
An EPD according to the related art, as illustrated in FIG. 2, is configured by including a lower substrate 11 in which a plurality of thin-film transistors (T) are formed and each of the thin-film transistors (T) is connected to a pixel electrode 29 formed in a matrix form; an electrophoretic film 50 adhered to the lower substrate 11; an upper substrate 61 adhered to the electrophoretic film 50 and a common electrode 63 formed on the surface thereof; and red (R), green (G), and blue (B) color filters 65a, 65b, 65c formed on the upper substrate 61 (Note: referring to FIG. 2, 65d is a white sub-pixel region, rather than a color filter).
Here, a passivation layer 25 is formed on an entire surface of the substrate including thin-film transistors (T) of the lower substrate 11.
In addition, a gate line (not shown) transmitting a scan signal to actively drive a plurality of thin-film transistors (T) and a data line (not shown) transmitting an image data signal are formed on the lower substrate 11.
At this time, the gate and data lines intersect each other to define pixels, and each pixel is provided with a thin-film transistor (T) and a storage capacitor (not shown), thereby performing a role of controlling a polarity of the voltage applied to each electrode and storing potential energy applied to the polarity.
Furthermore, a pixel electrode 29 electrically connected to the thin-film transistors (T) applies an electric field to the electrophoretic film 50.
In addition, the electrophoretic film 50 is composed of microcapsules 53 in which white particles 55a and black particles 55b are mixed with a solvent therewithin.
Furthermore, the red (R), green (G), and blue (B) color filters 65a, 65b, 65c are provided on the upper substrate 61, and the white sub-pixel region is not provided with a color filter but defined as a white sub-pixel region 65d. 
However, an electrophoretic display device according to the related art has a problem as follows.
In an electrophoretic display device according to the related art, a panel having a quad-type color filter structure to which a white sub-pixel is added has been used in order to enhance the problem of reduced white reflection rate in case of a color electrophoretic display device that uses color filters. Here, one pixel is composed of four dots, such as the red (R), green (G), blue (B), and white (W) dots, thereby causing the problem of reduced resolution. In particular, a quad-type color electrophoretic display device is formed by a structure having a small color filter area without black matrix, thereby causing a problem of reduced color characteristics.
As a result, in an electrophoretic display device according to the related art, color filters are used to fabricate a color EPD thereby showing a reflection reduction, and a white dot is additionally used to improve the problem thereby causing a resolution reduction.